I think I would do this.....
Any chance you can get AP you kind of have to do it! AP is a beast/monster....whatever you want to call him but he does the damage that 3-4 RB's do for fantasy! Turner is good to but I never really liked him that much. Last year he had some huge games and then had the cold games so he is and always will be a hit or miss.
I am not sure if this is a PPR league or not so that would make a pretty big difference as well since in PPR Welker/Moss combo is total domination. I do however think Marshall will turn around his week 1 performance (as well as about 100 other top studs who had poor week 1 performances) and be a nice WR to own this year. (BTW.....BMarsh didn't play preseason, is just learning the new plays and all and hasn't really worked with Orton much but Orton targeted Marshall quite a bit week 1).....now.....Marshall is by far no R.Moss, but he isn't far off (if he can get to the styles of last year) so.....
I would jump on this trade since it has you getting AP. Plus the fact that you have Welker and Moss (i don't like duel WR's very much even though this one is dominate but what if plays a big factor here)
I would make the trade!
Standard H2H 12 Team 1 Pt PPR, Start 1QB, 2RB, 2WR, 1 FLEX (RB/WR/TE), 1TE, 1K, 1 DEF